1. Field of the Invention
The present invention relates generally to an apparatus for reducing static electrical charges on the surface of an object and, more specifically, to an apparatus for reducing static electrical charges on the surface of a web of dielectric sheet material during its manufacture or handling.
2. Discussion of the Related Art
Static electrical charges are generated on a web of dielectric sheet material, such as paper and plastic, by contact with charged rollers or webs or by frictional contact with stationary guide surfaces necessary to transport the sheet through its manufacture or handling. The build-up of these charges can become a severe problem. Such static electrical charges can cause static electrical discharges, arcing, or sparks which can disrupt or damage nearby electronic equipment or affect the accuracy of sensors used in the manufacture or handling of such sheet materials. Additionally, the static electrical charges present on a web of dielectric sheet material may attract dust and dirt to the web and the manufacturing equipment, may pose a dangerous annoyance to operators of the equipment, or may present an explosion hazard in an explosive atmosphere. Thus, many types of devices have been used to reduce or remove such static electricity build-up from a web of sheet material during its manufacture or handling.
One such device is a contact neutralizer. These devices generally comprise a multiplicity of metal projections on an electrically grounded support which may be positioned transverse to the path of a sheet and be spaced so that the projections come into physical contact with successive sections of the surface of a passing sheet. These prior art devices have disadvantages in that they tend to scratch, mar or tear the surface of sheet material that has a delicate surface or coating. Also, the contact pressure that results between a passing sheet and the relatively stiff metallic projections of prior art contact neutralizers may tend to divert the path of the web of sheet material from its optimal intended path or to slow its speed, so that the manufacture or handling of such sheet material is not orderly and predictable. Similar difficulties are encountered when metallic grounding rollers are added along the path of a web of sheet material; and even when such rollers can be properly incorporated into the design of manufacturing or handling equipment, the cost of manufacturing and mounting such rollers may be relatively high.
Still other prior art devices known in the industry and used to neutralize static electrical charges from a web of sheet material are high-voltage and radioactive neutralizers. These devices ionize the air around an adjacent surface to afford a path to ground through the ionized air and the neutralizer to conduct away electrostatic charges on a surface contacted by the ionized air. One disadvantage of these devices is that they are relatively expensive to purchase, install and operate, as they require either a radioactive source, which requires occasional replacement, or a high voltage potential to be generated.